iPort/AI Communication Problem FAQ (Frequently Asked Questions)

There are two common communication problems when using the iPort/AI (#MIIC-202) host adapter. The first has to do with the UART used in the host computer RS-232 port. The second has to do with the setup of RS-232 flow control when you are writing a custom program.

16550 UART Issues

New PCs use the 16550 UART. This UART has a 16 byte FIFO buffer to help Windows, but it can cause problems with external RS-232 devices that have small buffers, such as the iPort/AI. Data in the UART Tx FIFO buffer is sent out by the host computer EVEN if RS-232 flow control is telling the host computer to stop. The iPort/AI, with its smaller buffer, needs the Tx FIFO buffer to be disabled.

The TX FIFO can be disabled from the Windows Device Manager. Access to the Device Manager is different for different versions of Windows (For Windows 2000 click, Start|Control Panel|System|Hardware|Device Manager|Ports|Communications Port (COMx)|Properties|Port Settings|Advanced...). After disabling the Tx FIFO buffer, YOU MUST power down and power up the PC for the change to take effect.

RS-232 Flow Control Issues

If you are developing a custom software application, and your application is receiving the /I90 response from the iPort/AI, this indicates you are overflowing the adapter's receive buffer. You should check your initialization code to make sure your application and the iPort/AI are using the same RS-232 flow control method (X-ON/X-OFF, or Hardware).

This is also true if you are using a terminal program like Windows Hyperterminal. Make sure the terminal properties are set correctly.

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